Lubricating compositions containing a complex sulfide of arsenic and antimony



United States Patent 3,377,277 LUBRICATING COMPOSITIONS CONTAINING A COMPLEX SULFIDE OF ARSENIC AND ANTIMONY John Richard Soulen, Narberth, P'a., assignor to Pennsalt Chemicals Corporation, Philadelphia, Pa., a corporation of Pennsylvania No Drawing. Filed Jan. 26, 1967, Ser. No. 611,824 8 Claims. (Cl. 252-12) ABSTRACT OF THE DISCLOSURE A complex sulfide of arsenic and antimony, having the approximate formula AsSbS is used as a solid lubricant composition for bearing surfaces, for example, either alone as a powder or film, or as an essential additive in conventional lubricant formulations such as greases and oils, or in a self-lubricating composite structure.

This invention relates to lubricant compositions comprising a complex sulfide of arsenic and antimony, and, more particularly, to lubricant compositions containing as an essential ingredient a complex sulfide having the approximate formula AsSbS This invention also concerns a method of lubricating a bearing surface which comprises applying thereto, as a lubricant, said complex sulfide of arsenic and antimony. The invention contemplates the use ofthe solid lubricant embodied herein as an essential additive for conventional lubricant compositions such as greases, oils and fluids, as well as being used alone in the finely-divided state, or as a thin film, and in self-lubricating composite structures.

Molybdenum disulfide in particulate form is generally regarded as the most versatile, efficient, and widely used solid lubricant material, either as an additive to enhance the properties of conventional lubricant compositions, or as a lubricant composition which is applied to a bearing surface in the form of dry powder or as a dispersion in a volatile liquid or as a film in combination with a resinous binder. It is known that the incorporation of a small proportion of finely powdered M08 into a conventional grease composition significantly enhances the bearing-wear characteristics and load-carrying capacity of said grease. It is also known that some other metallic sulfides perform a lubricating function between metal surfaces, for example, antimony pentasulfide, arsenic pentasulfide, complex zinc-antimony sulfide, stannic sulfide and the like (U.S. Patent No. 2,421,543). However, as stated previously, M052 is regarded as the best metallic sulfide lubricant known heretofore.

In accordance with the present invention, it has been discovered that a complex sulfide of arsenic and antimony having the approximate formula AsSbS, is significantly more efficient as a solid lubricant or lubricant additive than the metallic sulfides known previously. The complex sulfide embodied in this invention generally is incorporated in lubricant compositions in a particulate form, i.e., as a finely-divided powder having a particle size, in general, within the range of about 0.01 micron to about 100 microns, and preferably within the range of about 0.01 to 10 microns. The compositions embodied herein are useful for lubricating the contacting surfaces of a wide variety of materials, for example, metals such as steel, molybdenum, copper, zinc, bronze, brass, Monel and other metals and metal alloys, plastics, ceramics, graphite, and other materials, wherein the contacting surfaces may be of the same or different materials.

The complex sulfides embodied in this invention are amorphous, glass materials which are not composed of 3,377,277 Patented Apr. 9, 1968 the elemental constituents in specific integral atomic ratios, i.e., a range of compositions of the sulfides having varying atomic ratios of As, Sb and S are obtained using the preparative procedures described hereinafter. More specifically, the complex sulfides of this invention are represented by the formula As Sb S where x is within the range of about 0.7 to about 1.3, y is within the range of about 0.7 to about 1.3, and z is within the range of about 3 to about 5. In ideal preparations of the complex sulfide, the product is, however, essentially of the formula AsSbS and for purposes of convenience in this discussion the complex sulfides of the invention are referred to herein generally by the formula or approximate formula AsSbS This invention provides a grease composition having improved extreme pressure and load-carrying characteristics which is prepared by incorporating in a conventional grease from about 1 to 20 weight percent of the complex sulfide, preferably about 2 to about 10 percent, based on the weight of the total composition. The conventional grease can be a natural petroleum grease, which may contain small amounts of antioxidants, anti-corrosives, or other additives; or a synthetic grease comprised of a synthetic ester such as dioctyl sebacate, dioctyl adip'ate, tributyl phosphate, di-Z-ethyl hexyl sebacate, and the like, containing from about 5% to 45% of a thickener such as lithium stearate, aluminum stearate, lithium hydroxystearate, calcium stearate, silica, clay, and the like; and small amounts of other additives, such as antioxidants and anti-corrosion agents. Other greases which are improved by the complex sulfide are silicone greases comprised ofa silicone oil containing a thickening agent such as tetrafluoroethylene polymers and copolymers and other .fluoropolymers. The complex sulfide also finds utility as a component of a lubricating dispersion comprising a liquid oil carrier such as a hydrocarbon oil, synthetic ester oil, or silicone oil containing therein from about 0.5% to about 60% by weight of the solid sulfide particles, based on total weight of dispersion.

The solid lubricant of this invention can also be applied to the contacting surfaces as thin film. The methods of applying a thin film of solid lubricant are well known. For example, from about 1% to about 10% of the sulfide (based on total dispersion weight) is dispersed in a volatile solvent such as toluene, benzene, acetone, methyl ethyl ketone, etc. The dispersion is sprayed onto the bearing surface and the solvent is then evaporated leaving a film of lubricant. However, a preferred method of forming a thin film of the powdered sulfide lubricant on a bearing surface is to disperse the sulfide in a solution of a resinous binder material, for example, an epoxy resin, a phenolic resin, a silicone resin, or the like, in a suitable solvent for the resin such as toluene, zylene, butanol, methyl ethyl ketone and many other volatile, organic solvents, or mixtures of solvents for the binder resin. In general, the proportions of components may be from about 100 to 500 parts by weight of solvent, 5 to parts of complex sulfide, 10 to parts of resin, and optionally from 0.5 to 50 parts of other additives such as anti-oxidants, anti-corrosives and other solid lubricants. The mixture is sprayed onto the surface to be lubricated, the number of applications depending on the thickness of the film desired, generally on the order of from about 0.1 mil up to about 1 mil. The solvent is evaporated between successive film applications. The final step involves heating the surface to from about to about 800 F. to cure the resinous binder, the cure temperature depending on the kind of binder resin used.

Another formulation in which the complex sulfide embodied herein is employed as an essential component is in the self-lubricating, sintered-metal composite structure.

These structures, employed as bearings, self-lubricated sleeves, races, etc., are prepared by the well known techniques of metal powder molding. Briefly stated, a mixture of about 5% to about 50% by weight of the finelydivided sulfide and correspondingly from about 50% to about 95% of a finely-divided metal (e.g., copper, molybdenum, bronze, brass, or other metal or mixture of metals and/or alloys suitable for powder molding) having a particle size of from less than a micron to about 100 microns, is placed in an appropriate mold which is then subjected to a pressure that may range from about 10 to about 1000,000 lbs./ square inch, and heated to a sin-tering temperture of from about 100 F. to about 1200 F., the choice of pressure and temperature being governed by the specific metal or metals used.

The complex sulfide embodied herein may be prepared by either solution reaction-precipitation techniques or by fusion techniques. A typical preparation by the former technique is as follows. A hot (80-100 C.) solution of 1 part of AS203 in 9 parts of 5% aqueous sodium hydroxide solution is added slowly with stirring to 95 parts of a hot 5% aqueous solution of Na SbS -9H O. (Parts of materials as used throughout this specification refer to parts by weight). After stirring for about 30 minutes, the solution is slowly neutralized with vigorous stirring with about 30 parts of 5% aqueous hydrochloric acid solution until precipitation is complete. The orange-brown flocculant precipitate (about 3 parts of AsSbS is recovered by filtration, washed several times with hot water ununtil free of chloride ion, then with 95% ethanol solution, with hot CCL; and/ or CS until free of elemental sulfur, then with acetone, and alcohol, and finally dried in vacuo at about 110 C. As is typical of glassy materials, the complex sulfide of arsenic and antimony softens and coalesces over a wide temperature range rather than having a sharply defined melting point, usually over the range of about 200220 C. Elemental analysis of the amorphous product confirms the general formula assigned thereto. For example, elemental analyses of the products from four separate preparations were as follows (in weight percents);

AS Sb S No. 1 19. 5 40. l 38. 8 N0. 2 19. 42 35 No. 3 23. 6 37. 7 37. 6 N0. 4 21. 3 43. 35. 2

The theoretical elemental analysis calculated for the formula ASSbS4 is As, 23.1% Sb, 37.5% g. S, 39.5%.

The following describes a typical preparation of the complex sulfide by the fusion technique. A mixture of one part sulfur, 3.84 parts As S and 5.31 parts Sb S ground together by mortar and pestle and thoroughly mixed on a mixer mill, is heated isothermally in an evacuated sealed carius tube at 550 C. for 16 hours, and cooled at the normal cooling rate of the furnace. The

I homogeneous, amber glassy product (about 10 parts having a free sulfur content of less than 1% before washing) is ground to a fine powder which is washed several times with 5% HCl solution, water, hot CCl and/or CS acetone and finally 95 ethanol. The product, shown by elemental analysis to be essentially of the formula AsSbS is dried in vacuo at about 110 C. This fusion technique is also used to prepared AsSbS in a like manner with the following combination of starting materials; 2.5 parts sulfur, 3.84 parts AS233 and 3.82 parts Sb; 4 parts sulfur, 2.34 parts As and 3.82 parts Sb.

The examples next set forth illustrate and clarify the present invention.

Example I.Testing of AsSbS in grease composition Samples were prepared by homogeneously dispersing five percent by weight of a powdered solid lubricant in a grease composition consisting of a diester fluid containing up to lithium stearate as a thickener (the grease conformed to Military Specification MILG3278). The

Wear Scar Diameter in mm. at the following Sample Additive ad in 'g.

1 AS25 0 33 0.41 0. 1.26 1.44 1.51 2 A584 0.45 0.65 0.94 1.18 1.35 Weld 3 813283 0 35 0.70 1.18 1.30 1.49 1.52 4 SbzSs 0 34 0.44 0.92 "Weld 5 AsSbSi 0 33 0.45 0. 54 0.95 1.30 1.32

*Balls fused together.

The above data indicate that the rate of wear of the steel lubricated with compositions containing the complex sulfide, AsSbS is significantly les than that with the metallic sulfides of the prior art. In another series of tests, further wear load tests were carried out using the same base grease (Ml'L-G-3278) and the Shell 4-Ball test Apparatus as above-described and 5 wt. percent of a solid lubricant additive, except in the case of samples 6 and 7 which showed the performance of the unmodified base grease. These tests were conducted to measure the weld poin which is defined as the load at which the metal balls become fused together. The data are tabulated below:

Sample No. Additive Load at Weld Point in Kg.

None 80 None MoSz MOS: W581 200 S2 225 ASSbS4 (1) Weld point not reached at 355.

Example II.-Testing of AsSbS, in solid film composition.

Mixtures having consistencies suitable for spraying operations were prepared by wetting a sulfide powder with a solution of a phenolic resin binder (MILR3043) in a solvent therefore and thoroughly agitating the mixture. The solvent was a mixture of one part xylene, two parts methyl ethyl ketone and one part butyl alcohol. In order to compensate for density and particle size differences, an equal volume substitution" technique utilizing apparent densities was employed. (See M. J. Devine, E. R. Lamson and J. H. Bowen, Jr., J. Chem. and Eng. Data, 6, 79-82 (1961).) The steel V-block test specimens were first degreased in trichloroethylene vapor, then phosphated according to type M, class 3, under Military Specification MIL-P4623213. The specimens were then coated with each solid film lubricant to a film thickness of 0.00 to 0.0005 by spraying on 2 to 3 successive coats (allowing each to air dry before application of next), followed by air drying for 30 minutes, curing at approximately 150 C. for one hour, and cooling to ambient conditions.

The lubricating properties (wear or endurance life) were determined by a modification of a technique described in Federal Test Method Standard No. 791a, Method 3807, employing a Falex Lubricant Tester" apparatus which provides for sliding friction of an unlubricated degreased cylindrical pin rotating, under load, against two solid film lubricated A1SIC-ll37 steel V- blocks. Wear life tests were conducted at C., 290 r.p.m., and 1000 lbs. (gauge) load, after preliminary break-ins, by automatically increasing to 300 lbs., releasing load, then stepping up loads in 250 lb. increments for 3 minutes at each load, until the test load was reached. Both AlSI-C-3135 steel pins and molybdenum pins were used. Failure was indicated by an increase in torque of 5-inch-lbs. above a steady state value or by breakage of the shear pin (which holds the test pin), or by seizure or breakage of the test pin.

The results presented below readily show the superiority of the AsSbS as a solid lubricant.

Wear life in minutes for Apparent Approxia Pin Material of- Sample No. Sulfide density of mate wt. sulfide, percent of Steel Molybdenum q./ce. sulfide in film In another series of tests, a solid film lubricant composition comprised of about wt. percent of phenolic resin (Military Specification MIL-R-3943) and about 15 wt. percent of AsSbS was subjected to a wear life test on the Falex Lubricant Testerand compared to other metallic sulfides dispersed in a phenolic resin composition in the same manner using equal volume substitutions as described in the paper The Effect of the Chemical Composition of Metals on Solid Lubrication by Devine, Lamson and Bowen, Preprints, Amer. Chem. Soc., Div. Petroleum Chem., Los Angeles Meeting, pp. C-177 to C-188, March 31-April 5, 1963. The results and comparisons are presented below wherein the wear life is measured as the time required to obtain a failure as determined by a torque rise and/or breakage of the shear pin.

Wear life in minutes for a Pin Material of Sulfide Molybdenum Steel 1 Test stopped at 245.

Example III.--Testing of AsSbS; in a self-lubricating composite structure.

A self-lubricating solid composite comprised of /3 of powdered AsSbS /3 of finely-divided copper and /3 of finely-divided molybdenum was prepared by mixing said powders and hot-pressing the mixture into a sintered shape. The composite was machined into a rectangular test block and evaluated using the Alpha Molykote LFW- 1 Lubricant Test Apparatus. This test employs a Timken bearing outer steel race rotated under load against the composite test block at 72 r.p.m. and lbs. radial load at a temperature of 77 F. The composite sustained 3555 revolutions before failure, indicating highly efiicient lubrication.

It is to be understood that the foregoing examples are presented for the purpose of illustrating the invention and should not be construed to limit the scope thereof as defined by the appended claims, the invention residing in the provision of the complex sulfide embodied herein as an essential component of lubricant compositions, the other optional components of which can vary widely in type and proportions.

I claim:

1. A lubricant composition containing as an essential ingredient a complex sulfide of arsenic and antimony of the formula As Sb S where x is within the range of about 0.7 to about 1.3, y is within the range of about 0.7 to about 1.3, and z is within the range of about 3 to about 5.

2. The composition in accordance with claim 1 wherein the complex sulfide is essentially AsSbS 3. A composition according to claim 1 comprising a grease or oil containing the complex sulfide in particulate form dispersed therein.

4. A composition in accordance with claim 3 wherein the complex sulfide is essentially AsSbS 5. A composition according to claim 1 comprising a thin film of the complex sulfide with a resinous binder material.

6. A composition according to claim 5 wherein the complex sulfide is essentially AsSbS 7. A composition according to claim 1 comprising a sintered-metal composite containing the complex sulfide admixed therein.

8. A composition according to claim 7 wherein the complex sulfide is essentially AsSbS DANIELE. WYMAN, Primary Examiner. I. VAUGHN, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3 ,377 ,277 April 9 1968 John Richard Soulen It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, line 11, "1000,000" should read 100,000 line 29, cancel "un"; line 63, "prepared" should read prepare Column 4, line 3, "79a" should read 791 line 8, "l800" should read 1800 line 23, "les" should read less line 46, "oher" should read other line 64, "0.002" should read 0.0002 Column 5, line 30, "MIL-R-3943" should read MIL-R-3043 Signed and sealed this 21st day of October 1969.

(SEAL) Attest:

Edward M. Fletcher, Jr. E.

Attesting Officer Commissioner of Patents 

